Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already flag this as destructiveHint=true, so the agent knows it mutates state; the description adds the return value ('Returns the updated attendance') and the underlying endpoint, which is genuinely useful given there is no output schema. It stops short of explaining why a check-in is flagged destructive, whether it is reversible (e.g., via unregister), or any permission requirements.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two clauses plus an endpoint reference, front-loaded with the action and its plain-language synonym. Every element earns its place; only the trailing API path is arguably redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter mutation with no output schema, the description covers the action and the return value, but the destructiveHint is left unexplained and there is no note on prerequisites, idempotency, or reversibility. Adequate but with clear gaps for a write operation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% - both event_id and customer are documented as numeric ids in the schema - so the description adds nothing about parameters. Baseline 3 applies when the schema carries the full parameter burden.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ('confirm that a customer attended an event') and even clarifies with the synonym 'check them in', so an agent immediately knows this marks attendance rather than merely reading it. It does not, however, explicitly contrast itself with the sibling tools register_customer_for_event or unregister_customer_from_event, which all touch the same event/customer pair.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no when-to-use guidance: nothing tells the agent that this applies after a customer attended (vs. registering them beforehand), nor when to prefer it over the similar-sounding register/unregister siblings. The parenthetical '(check them in)' implies context but does not state conditions or exclusions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.